The present invention relates to an intake air control system and method for an internal combustion engine.
An example of an intake throttle valve control system for an internal combustion engine that controls an opening degree of an intake throttle valve by a feedback of an intake air quantity so that an actual intake air quantity becomes equal to a target intake air quantity is disclosed in Japanese Patent Second Publication (after examined) No. 2-5898.
A variation of an EGR quantity causes a variation of a pressure differential across an intake throttle valve. Thus, if the opening degree of the intake throttle valve is constant, a variation of the EGR quantity causes the actual intake air quantity to vary relative to the target intake air quantity. The earlier technology disclosed in the above described publication can control the opening degree of the intake throttle valve according to a variation of the actual intake air quantity relative to the target intake air quantity, so that the actual intake air quantity becomes equal to the target intake air quantity after lapse of a certain time.
However, by the above-described earlier technology, the feedback control of the intake air quantity is not executed unless the actual intake air quantity becomes different from the target intake air quantity, thus causing a problem that immediately after a variation of the EGR quantity the actual intake air quantity is always caused to deviate from the target intake air quantity.
It is accordingly an object of the present invention to provide an intake air control system and method for an internal combustion engine that can executes a highly accurate intake air quantity control while executing an EGR control.
To achieve the above object, there is provided according to an aspect of the present invention an intake air control system for an internal combustion engine comprising an intake throttle valve that controls an intake air quantity of air flowing into the engine, an EGR valve that controls a quantity of exhaust gas recirculated back to an intake system portion of the engine downstream of the intake throttle valve, and a control unit that controls the intake throttle valve and the EGR valve in accordance with an operating condition of the engine, the control unit including a target opening area calculating section that calculates a target opening area of the intake throttle valve based on a target EGR ratio corresponding to the operating condition of the engine, and a control section that controls an opening degree of the intake throttle valve based on the target opening area.
According to another aspect of the present invention, there is provided an intake air control system for an internal combustion engine comprising an intake throttle valve that controls an intake air quantity of air flowing into the engine, an EGR valve that controls a quantity of exhaust gas recirculated back to an intake system portion of the engine downstream of the intake throttle valve, calculating means for calculating a target opening area of the intake throttle valve based on a target EGR ratio corresponding to the operating condition of the engine, and control means for controlling an opening degree of the intake throttle valve based on the target opening area.
According to a further aspect of the present invention, there is provided an intake air control method for an internal combustion engine having an intake throttle valve that controls an intake air quantity of air flowing into the engine, and an EGR valve that controls a quantity of exhaust gas recirculated back to an intake system portion of the engine downstream of the intake throttle valve, the method comprising calculating a target opening area of the intake throttle valve based on a target EGR ratio corresponding to an operating condition of the engine, and controlling an opening degree of the intake throttle valve based on the target opening area.